The present disclosure relates to a photometric device measuring luminance, chromaticity, spectral distribution, etc. of light emitted from a measuring object.
In recent years, photometric devices have been used in various fields such as industrial, food, and medical areas: measuring display characteristics of a liquid crystal display, or a state of coating on a product such as an automobile; measuring freshness of foods; and measuring health conditions of humans and animals.
Photometric devices adopt various methods for measurement of light. Examples of the methods include using filters. For example, a photometric device with multiple filters is known. The photometric device of this type includes optical filters (interference filters) corresponding to the tristimulus values to measure light emitted from a measuring object (see Japanese Unexamined Patent Publication No. H6-201472).
A photometric device with a transmissive wavelength variable filter (also called a scanning wedge band pass filter or a linear variable filter) having transmitting portions each corresponding to a different transmissive wavelength is also developed to implement measurement (see Japanese Unexamined Patent Publication No. 2006-177812).
The technique of Japanese Unexamined Patent Publication No. H6-201472 adopts the X, Y, and Z filters adjusted to but not completely conformed to the color matching functions. Thus, the measurement speed is fast, but the measurement accuracy is low.
On the other hand, the technique of Japanese Unexamined Patent Publication No. 2006-177812 adopts the transmissive wavelength variable filter to scan the one filter to obtain spectral characteristics in a necessary wavelength range. However, the transmissive wavelength variable filter splits light for every wavelength by plane split. Thus, the amount of light into a photoreceptor is very small, and low luminance (black luminance) cannot be measured. That is, this method is unsuitable for measurement of light of a liquid crystal display where evaluation of black luminance is important.
As such, Japanese Unexamined Patent Publication No. H6-201472 and Japanese Unexamined Patent Publication No. 2006-177812 disclose the methods each having both the merit and the demerit, and it is not easy for a photometric device to make measurement of light from low luminance to high luminance with high accuracy in short time.
In view of the foregoing, it is an object of the present disclosure to provide a photometric device that can make measurement of light from low luminance to high luminance with high accuracy in short time.